Motor and the compressor including the same

ABSTRACT

A motor, namely, a motor with minimum loss and improved efficiency is disclosed. More specifically, a motor having enhanced starting torque performance and increased normal operation efficiency is disclosed. In the motor in which a rotor is started using induction torque generated as power is supplied to a coil of a stator, the rotor includes a rotor core, a plurality of conductive bars arranged, along a circumferential direction, in an outer rim region of the rotor core, to generate an induction current, magnets provided in the rotor core, to generate a magnetic flux, for generation of a magnetic torque, and end-rings provided at the top and bottom of the rotor core to have no interference with the magnets, the end-rings being connected with the plurality of conductive bars.

This application is a National Stage Entry of International ApplicationNo. PCT/KR2008/001324, filed Mar. 7, 2008, and claims priority to KoreanPatent Application No. 10-2007-0023514, filed in Korea on Mar. 9, 2007,each of which is hereby incorporated by reference in its entirety as iffully set forth herein.

TECHNICAL FIELD

The present invention relates to a motor, and more particularly, to amotor with minimum loss and improved efficiency while achieving enhancedstarting torque performance and increased normal operation efficiency.

In addition, the present invention relates to a motor which iseffectively applicable to variable load, and a variable capacitycompressor using the motor.

BACKGROUND ART

In general, a single-phase induction motor includes a stator, on which amain coil and an auxiliary coil are wound with a spatial interval of 90degrees therebetween. A source voltage is applied directly to the maincoil, and also, is applied to the auxiliary coil via a capacitor and aswitch. This is because the main coil cannot generate a starting forcealone even if a voltage is applied thereto. Therefore, with theassistance of a start device such as the auxiliary coil, etc., thestator generates a rotating magnetic field to start the rotor.

The start device is classified, according to the kind thereof, into asplit-phase type, shading-coil type, capacitor-start type,repulsive-start type, and the like.

As an example of a single-phase induction motor having theabove-described start device, a capacitor-start type single-phaseinduction motor is illustrated in FIGS. 1 and 2.

FIG. 1 illustrates a stator and a rotor of a general single-phaseinduction motor, and FIG. 2 illustrates a simplified circuit of therotor and stator coils.

When only a main coil 12 is wound on a stator 10, the stator 10generates only an alternating magnetic field, and thus, starting of arotor 20 is not accomplished. For this reason, an auxiliary coil 14 mustbe wound on the stator 10 to generate a rotating magnetic field. Withthe rotating magnetic field, the rotor can be started and rotated in apredetermined direction. Namely, starting torque arises via the rotatingmagnetic field.

In the simplified circuit of FIG. 2, a capacitor 15 serves to delay aphase of current to be applied to the auxiliary coil 14, so as togenerate starting torque via interaction between the auxiliary coil 14and the main coil 12. Once being started, rotation of the rotor 20 ismaintained, under an assumption of no load variation, even if power isnot applied to the auxiliary coil 14. Namely, it is unnecessary to applypower to the auxiliary coil 14 if the rotor 20 maintains a predeterminedor more revolutions per minute after being started. However, when loadvaries, additional starting torque is required. Therefore, it ispreferable that power always be supplied to the auxiliary coil 14 viathe capacitor 15.

Of course, a three-phase induction motor can generate a rotatingmagnetic field even when only a main coil is wound on a stator, and doesnot require winding of the above-described auxiliary coil on the stator.That is, the three-phase induction motor does not require a separatestart device.

An advantage of the above-described single-phase induction motor is thatit does not require an inverter like a brushless DC (BLDC) motor orreluctance motor and can be started directly using single-phasecommercial power, resulting in superior price competitiveness.

Now, the above-described general single-phase induction motor will bedescribed in detail with reference to FIGS. 1 and 2.

The stator 10, which has a hollow internal configuration, includes aplurality of teeth 11 arranged, along an inner circumference thereof bya desired angular interval, to protrude radially inward, and a main coil12 wound on the respective teeth 11 to have a polarity of N-pole orS-pole upon primary application of a current.

Here, an insulator (not shown) is interposed between the teeth 11 andthe main coil 12. The insulator serves not only to provide electricalinsulation between the teeth 11 and the main coil 12, but also tofacilitate easy winding of the main coil 12.

The stator 10 further includes an auxiliary coil 14, which is wound onthe stator 10 to have a desired spatial angular interval with the maincoil 12 and is adapted to generate a rotating magnetic field uponapplication of a current. Of course, the auxiliary coil 14 is also woundon the teeth 11 by interposing an insulator therebetween. The main coil12 and auxiliary coil 14 can be called together “stator coils” or simply“coils”.

The coils 12 and 14 are connected to a single-phase power source, and atthe same time, are connected in parallel to each other. The capacitor 15is connected to the auxiliary coil 14 in series. Again, although notshown, the capacitor 15 may be optionally connected to the power sourcevia a switch.

Generally, the rotor 20 may be a frequently used squirrel cage rotor.FIGS. 1 and 2 illustrate the squirrel cage rotor.

The rotor 20 is normally fabricated by stacking steel plates one aboveanother to constitute a rotor core, and each steel plate is formed,along an outer circumference thereof, with a plurality of slots 21 atdesired radial positions from the center of the steel plate by a desiredangular interval. The rotor 20 further includes rod-shaped conductivebars 22 inserted into the respective slots 21 of the rotor core. Therod-shaped conductive bars 22 are normally made of copper or aluminumrods.

Both ends of the squirrel cage rotor core are connected with not-shownend-rings (See FIGS. 13 and 14), to achieve electric connection via theconductive bars 22, and the end-rings are generally formed via aluminumdie-casting. Specifically, the conductive bars 22 and end-rings areintegrally formed with each other via aluminum the casting, and both theend-rings are located, respectively, at the top and bottom of the rotorcore.

Meanwhile, the rotor 20 is centrally provided with a shaft hole 24. Arotating shaft (not shown) to transmit a rotating force of the rotor 20to an external component will be press-fitted into the shaft hole 24,such that the rotor 20 and rotating shaft constitute a unitary rotatingbody.

In operation of the above-described single-phase induction motor, ifpower is applied to the coils, an induction current is generated in theconductive bars 22, causing the rotor 20 to be rotated by resultinginduction torque. However, in this case, the conductive bars 22 causeloss, namely, conductive bar loss. Due to the conductive bar loss,therefore, improvement in efficiency of a motor of a predetermined sizeis limited. The single-phase induction motor is problematic whenhigh-efficiency is required.

Other problems of the conductive bar loss include an increase in thetemperature of the rotor 20 and a great variation of loss depending onthe temperature variation. In particular, the higher the temperature,the greater the conductive bar loss. For this reason, improvement inmotor efficiency at high temperature is limited.

Meanwhile, the single-phase induction motor, in consideration ofcharacteristics thereof, must always be operated at a lower speed thansynchronous speed, in order to generate induction torque. This isbecause the single-phase induction motor theoretically has zero torqueat the synchronous speed, and the smaller the rotating speed, thegreater the torque.

Accordingly, in the single-phase induction motor, as motor load, namely,load applied to the rotating shaft varies, a rotating speed of therotating shaft, namely, a rotating speed of the motor varies, and thismakes it difficult to control the motor depending in consideration ofload variation.

DISCLOSURE OF INVENTION Technical Problem

An object of the present invention devised to solve the problems lies ona motor, which can solve the above-described problems of a single-phaseinduction motor.

Another object of the present invention devised to solve the problemlies on a motor having improved efficiency, and more particularly, on amotor which can operate at synchronous speed during normal operation,and consequently, can achieve maximum normal operation efficiency.

A further object of the present invention devised to solve the problemlies on a motor, which can always operate at synchronous speed even ifmotor load varies during normal operation, resulting in easy motorcontrol.

A still further object of the present invention devised to solve theproblem lies on a motor, which can achieve maximum efficiency, inparticular, at high temperature.

A still further object of the present invention devised to solve theproblem lies on a motor, which has starting characteristics of a generalsingle-phase induction motor without using an inverter, therebyachieving reduced manufacturing costs.

A still further object of the present invention devised to solve theproblem lies on a compressor, which can achieve improved efficiency andfacilitate variable capacity operation thereof via the use of theabove-described motor.

Technical Solution

The objects of the present invention can be achieved by providing amotor, in which a rotor is started using an induction torque generatedas power is supplied to a coil of a stator, wherein the rotor comprises:a rotor core; conductive bars arranged, along a circumferentialdirection, in an outer rim region of the rotor core, to generate aninduction current; flux barriers formed in the rotor core, to interruptflow of a magnetic flux, for generation of a reluctance torque; andmagnets provided in the rotor core, to generate a magnetic flux, forgeneration of a magnetic torque.

Here, the rotor may be started using an induction torque generated bythe conductive bars, and, once started, may be rotated using thereluctance torque generated by the flux barriers and the magnetic torquegenerated by the magnets. In addition, the rotor, once started, may berotated at synchronous speed using the reluctance torque and themagnetic torque.

Specifically, the motor according to the present invention has startingcharacteristics of a general induction motor upon starting of the rotor,and once started, has rotating characteristics of a synchronous motor.The motor according to the present invention, once started, is rotatedat synchronous speed using the reluctance torque and the magnetic torqueduring normal operation, and can achieve high efficiency. Accordingly,it is possible to provide a high-efficiency motor without complex motorstarting components.

The induction torque may be generated by a rotating magnetic fieldgenerated in the stator and the induction current generated in therotor. Accordingly, it is unnecessary to supply three-phase power to thecoil. Namely, single-phase power can be supplied, similar to a generalsingle-phase induction motor.

When the single-phase power is supplied to the coil, the coil preferablyincludes a main winding and an auxiliary winding, for starting of therotor. Of course, although such a starting configuration can be changedvariously, the following description is limited to a capacitor-starttype induction motor for the convenience of description.

When the capacitor-start type induction motor is applied to the presentinvention, the main winding and the auxiliary winding are connected to asingle-phase power source while being connected in parallel to eachother. In addition, a capacitor is connected to the auxiliary winding inseries.

Preferably, the flux barriers are arranged to provide the rotor with atleast two or more even numbers of poles. With the flux barriers, therotor may be provided with a q-axis extending radially from a center ofthe rotor, along which the flow of a magnetic flux is interrupted by theflux barriers, and a d-axis extending radially from the center of therotor, along which the flow of a magnetic flux is not interrupted.

For example, when the rotor includes two poles, the q-axis and thed-axis may be spatially orthogonal to each other. Preferably, the fluxbarriers are symmetrical about the q-axis.

Preferably, each flux barrier is tilted, about the center of the rotor,from the center to both ends thereof such that both the ends of the fluxbarrier are far away from or closer to an axis orthogonal to the q-axis.This has the effect of further increasing an occupation rate of the fluxbarriers in a direction of the q-axis of the rotor core, thereby furtherincreasing reluctance in the q-axis direction. Preferably, the fluxbarriers, constituting each pole, are arranged in at least two or morelayers.

The flux barrier of each layer may be continuously formed, and the fluxbarriers, from the outside nearer to the inside of the rotor, may have alonger length.

The magnets may be inserted into a partial region of the respective fluxbarriers. The magnets may include at least two or more magnets arrangedin a longitudinal direction of the respective flux barriers. Of course,the magnets may include at least two or more magnets arranged in alongitudinal direction of the rotor. In this case, preferably, themagnets include unit magnets having the same shape as one another.

Preferably, each flux barrier is formed with a stepped portion todetermine insertion positions of the associated magnets.

Preferably, an imaginary line, which connects corresponding tip ends ofthe magnets inserted in the respective layers of flux barriers, isparallel to the q-axis. With this arrangement of the tip ends of themagnets, the greatest magnetic flux can be generated on the basis of theq-axis. In addition, the total magnetic flux, generated by all themagnets, can take the form of a square wave rather than a sine wave.

The arrangement of the magnets enables generation of greater magnetictorque on the basis of the q-axis and, as will be described hereinafter,permits an increase in a radial width of end-rings. The increased radialwidth of the end-rings has the effect of reducing loss due to thepresence of end-rings.

Of the conductive bars, preferably, a radial width of the conductivebars, which are arranged within an angle defined between the center ofthe rotor and both ends of an outermost flux barrier, is smaller thanthat of other conductive bars. This is because as the radial width ofthe conductive bars is increased, a flow path of the magnetic flux nearthe conductive bars becomes extremely narrow. This reduces a reluctancetorque due to premature saturation of the magnetic flux.

Preferably, both ends of the respective flux barriers are arrangedclosely opposite the adjacent conductive bars, to minimize leakage ofmagnetic flux through gaps between the flux barriers and the conductivebars. Preferably, the ends of each flux barrier have a smaller widththan that of the remaining portion of the flux barrier. This is because,when forming the conductive bars and end-rings via aluminum die-casting,molten aluminum may be introduced into the flux barriers upon receivinga pressure.

In another aspect of the present invention, provided herein is a motorin which a rotor is started using induction torque generated as power issupplied to a coil of a stator, wherein the rotor comprises: a rotorcore; a plurality of conductive bars arranged, along a circumferentialdirection, in an outer rim region of the rotor core, to generate aninduction current; a magnet provided in the rotor core, to generate amagnetic flux, for generation of magnetic torque; and end-rings providedat the top and bottom of the rotor core to have no interference with themagnet, the end-rings being connected with the plurality of conductivebars.

In a further aspect of the present invention, provided herein is amotor, in which a rotor is started using induction torque generated aspower is supplied to a coil of a stator, wherein the rotor comprises: arotor core; a plurality of conductive bars arranged, along acircumferential direction, in an outer rim region of the rotor core, togenerate an induction current; a flux barrier formed in the rotor core,to interrupt flow of a magnetic flux, for generation of reluctancetorque; and end-rings provided at the top and bottom of the rotor coreto have no interference with the flux barrier, the end-rings beingconnected with the plurality of conductive bars.

That is, the motor according to the present invention may have any oneof the flux barrier and the magnet, or may include both of them.However, in either case, it is preferable that the end-rings be providedto have no interference with the flux barrier and/or the magnet.Accordingly, the end-rings can be applied to the above-described aspectof the present invention.

In a still further aspect of the present invention, provided herein area compressor including the above-described motor and a method forcontrolling the same.

Here, the rotor included in the compressor has features in that a rotoris started by induction torque generated as single-phase power issupplied to a coil of a stator, and once rotated, is rotated atsynchronous speed, and that the coil includes a main winding connectedwith a single-phase power source for supply of the single-phase powerand an auxiliary winding connected parallel to the main winding whilebeing connected with the single-phase power source, and capacitors,connected parallel to each other, are connected to the auxiliary windingin series.

Preferably, any one of the capacitors is selectively electricallyconnected with the auxiliary winding via a switch. The switch ispreferably selectively turned on according to load variation of themotor. For example, the switch may be turned on under high motor load,and may be turned off under low motor load. In addition, the switch canbe kept on during initial starting of the motor.

The compressor may be a variable capacity compressor in which a singlemotor is operated to compress a refrigerant. Here, initial starting ofthe compressor means initial starting of the motor.

The variable capacity compressor includes a cylinder in which therefrigerant is compressed. As the quantity of the refrigerant to becompressed in the cylinder varies according to motor load, a capacity ofthe compressor can vary. The capacity of the compressor may also vary asonly a part of a plurality of cylinders are optionally operated or allthe cylinders are operated.

The compressor can always begin to operate under a low load condition,regardless of an initial operating condition.

ADVANTAGEOUS EFFECTS

According to the present invention, a motor having improved efficiencyand a variable capacity compressor using the same can be accomplished.

More specifically, according to the present invention, it is possible toprovide a motor, which operates at synchronous speed, in particular,during normal operation, thereby achieving maximum normal operationefficiency.

Further, according to the present invention, even if motor load variesduring normal operation, the motor can always operate at synchronousspeed. As a result, it is possible to provide a motor, which is easy tocontrol and has maximum efficiency, in particular, at high temperature.

According to the present invention, the motor can achieve startingcharacteristics of a general single-phase induction motor without usingan inverter, resulting in a reduction in manufacturing costs thereof.

Furthermore, according to the present invention, startingcharacteristics of the motor can be enhanced regardless of initial load,to rapidly reach normal operation. As a result, a motor, which can varya capacity and thus, achieve high efficiency during normal operation,and a variable capacity compressor using the motor can be accomplished.Also, in consideration of a compressor's high internal temperature, itis possible to provide a compressor achieving high-efficiencyperformance even at high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a sectional view illustrating a rotor and a stator of aconventional induction motor.

FIG. 2 is a conceptual view schematically illustrating a rotor andstator coils of the conventional induction motor.

FIG. 3 is a conceptual view schematically illustrating a rotor andstator coil circuit of a motor according to the present invention.

FIG. 4 is an enlarged sectional view illustrating a part of the rotorshown in FIG. 3.

FIGS. 5 to 7 are sectional views illustrating different embodimentsrelated to the shape of a tip-end of a flux barrier shown in FIG. 3.

FIG. 8 is an exploded perspective view illustrating a rotor core of amotor according to the present invention.

FIG. 9 is a plan view illustrating configuration of an uppermost unitrotor core of a motor according to an embodiment of the presentinvention;

FIG. 10 is a plan view illustrating a lowermost unit rotor core of amotor according to an embodiment of the present invention, or a planview illustrating an uppermost unit rotor core of a motor according toanother embodiment of the present invention.

FIG. 11 is a top plan view illustrating a rotor of a motor according toan embodiment of the present invention.

FIG. 12 is a top plan view illustrating a rotor of a motor according toan embodiment of the present invention, or a bottom plan viewillustrating a rotor of a motor according to another embodiment of thepresent invention.

FIG. 13 is a perspective view illustrating an upper end-ring of a motoraccording to an embodiment of the present invention.

FIG. 14 is a perspective view illustrating a lower end-ring of a motoraccording to an embodiment of the present invention, or a perspectiveview illustrating an upper end-ring of a motor according to anotherembodiment of the present invention.

FIG. 15 is a graph illustrating the relationship between motor'sstarting torque and capacitor value.

FIG. 16 is a circuit diagram schematically illustrating a part of astator coil circuit, under high motor load, according to the presentinvention.

FIG. 17 is a circuit diagram schematically illustrating a part of astator coil circuit, under low motor load, according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to a motor according to the presentinvention, examples of which are illustrated in the accompanyingdrawings of FIGS. 3 to 15. In addition, for the convenience ofdescription, an inner type motor, in which a rotor is rotatable inside astator, will be described hereinafter. However, the motor according tothe present invention is not essentially limited to the inner typemotor.

The motor according to the present invention is a motor, in which arotor is started using an induction torque, and therefore, can take thesame configuration as that of a conventional general induction motor.Specifically, referring to FIG. 3 illustrating the configuration of aninduction motor according to the present invention, the induction motorcan include a rotor 120 provided with slots 121 and conductive bars 122,and stator coils 112 and 114 (hereinafter, referred to as “coils”) and acapacitor 115 for rotation of the motor, etc. Hereinafter, a detaileddescription of overlapped configurations will be omitted.

Note that the motor according to the present invention can furtherinclude flux barriers 140, which are formed in a rotor core to interruptthe flow of a magnetic flux, for generation of reluctance torque. Inaddition, the motor according to the present invention can furtherinclude magnets 130, which are embedded in the rotor core to generate amagnetic flux, for generation of magnetic torque.

With the above-described configuration, according to the presentinvention, it is possible to provide a motor, which can be started onthe basis of characteristics of an induction motor, and also, can beoperated on the basis of characteristics of a synchronous motor duringnormal operation. In other words, after being started, the rotor can berotated at synchronous speed using the reluctance torque and themagnetic torque. Hence, according to the present invention, it ispossible to eliminate complex and expensive components, such as a startinverter, etc., differently from a general synchronous motor.

Now, the principle of generating the reluctance torque and the magnetictorque in the motor according to the present invention will be describedin detail with reference to FIG. 3.

First, reluctance torque will be described in detail.

As shown in FIG. 3, the flux barriers 140 are arranged along a q-axis.Here, the flux barriers 140 are formed by removing partial regions of arotor core 123 that is made of a magnetic substance. Specifically, airlayers can be created via the flux barriers 140, and non-magneticsubstances, for example, resin substances can be filled in the fluxbarriers 140.

When a current is applied to the coils to form a magnetic pole, amagnetic flux is generated in the rotor. However, due to the fluxbarriers 140, extremely high reluctance is generated in the q-axis,along which the flux barriers 140 are arranged. Conversely, extremelylow reluctance is generated in a d-axis, along which no flux barrier isprovided.

Accordingly, the rotor will rotate in a direction to minimize reluctancedifference between directions of the q-axis and d-axis. Force causingsuch a rotation of the rotor is called reluctance torque. The greaterthe reluctance difference, the greater the magnitude of reluctancetorque.

Meanwhile, as shown in FIG. 3, the motor according to the presentinvention includes the magnets 130. If a current is applied to the coilsto form a north magnetic pole, the magnets 130 can be magnetized tobecome a south pole. Specifically, in an arrangement of the rotor asshown in FIG. 3, a magnetic flux due to the stator and a magnetic fluxdue to the magnets 130 offset each other, resulting in greaterreluctance of the q-axis direction. Accordingly, as compared to theabsence of the magnets, greater reluctance difference between the q-axisand d-axis directions can be accomplished. Consequently, using themagnets can increase reluctance torque.

The magnets can generate magnetic torque by interaction with the stator.Specifically, if a current is applied to the coils to form a magneticpole, the magnetic pole of the stator and the magnetic pole of themagnet interact with each other according to a relative position betweenthe rotor and the magnet, resulting in generation of magnetic torque.

As described above, after being started, the motor according to thepresent invention carries out a synchronous rotation using reluctancetorque and magnetic torque, thereby achieving extremely high efficiencyduring normal operation. This means that, assuming identical motor sizeand identical current strength, the motor according to the presentinvention can achieve extremely high efficiency as compared to a generalinduction motor.

Hereinafter, configuration of the rotor included in the motor accordingto the present invention will be described in detail with reference toFIGS. 3 to 5.

The rotor 120 includes the rotor core 123 as a basic body, and the fluxbarriers 140 formed in the rotor 120, more particularly, formed in therotor core 123.

The q-axis extends radially from the center of the rotor through theflux barriers 140, along which the flow of a magnetic flux isinterrupted. Also, the d-axis extends radially from the center of therotor, along which no interruption in the flow of a magnetic fluxoccurs.

Here, the flux barriers can be arranged to form at least two evennumbers of poles along a circumferential direction of the rotor. Thisarrangement is shown in FIG. 3. Specifically, when the flux barriers arearranged to form two poles, as shown in FIG. 3, the q-axis and thed-axis are spatially orthogonal to each other. Also, when the fluxbarriers are arranged to form four poles, although not shown, the q-axisand the d-axis have a spatial interval of 45 degrees.

Preferably, as shown in FIG. 3, each flux barrier 140 is symmetricalabout the q-axis. This configuration permits reluctance torque to besymmetrical about the q-axis, thereby preventing noise or vibration dueto deviation of the reluctance torque.

And, preferably, the flux barriers 140 are arranged in at least two ormore layers. More specifically, it is preferable that at least two ormore layers of flux barriers be arranged at each of an upper half planeand a lower half plane of the rotor shown in FIG. 3. This increases anoccupation rate of the flux barriers 140 in the q-axis direction of therotor core 123, thereby further increasing reluctance in the q-axisdirection.

For the same reason, preferably, each flux barrier 140 is tilted, aboutthe center of the rotor 120, from the center to both ends thereof suchthat both the ends of the flux barrier 140 are far away from or closerto an axis orthogonal to the q-axis. More specifically, as shown in FIG.3, it is preferable that the flux barrier 140 be bulge upward ordownward on the basis of the d-axis, rather than being parallel to thed-axis. The flux barrier may have an angled shape or arched shape.

Of the flux barriers 140, as shown in FIG. 3, the flux barriers 140nearer to the center of the rotor, namely, nearer to the insidepreferably have a longer length. This increases reluctance in the q-axisdirection, and consequently, can maximize reluctance difference betweenthe q-axis and d-axis directions.

Preferably, a radial width of the conductive bars 122, which arearranged within an angle α defined between the center of the rotor andboth ends of an outermost flux barrier 140, is smaller than that ofother conductive bars 122.

When the conductive bars 122 within the angle α have a large radialwidth as shown in FIG. 3, a distance between these conductive bars 122and the adjacent flux barrier 140 becomes extremely narrow. Thisdisadvantageously increases a possibility of leakage of a magnetic fluxdue to magnetic flux saturation in the d-axis direction. Therefore, toassure a sufficient distance between the conductive bars 122 and theflux barrier 140, it is preferable to reduce the radial width of theconductive bars 122 arranged within the angle α.

Meanwhile, as shown in FIGS. 4 and 5, it is preferable that both ends ofthe respective flux barriers 140 be positioned closely opposite theadjacent slots 121. Specifically, it is preferable to minimize adistance between both ends of the respective flux barriers 140 and theadjacent slots 121. This is to prevent a magnetic flux generated alongthe d-axis from leaking through gaps between the flux barriers 140 andthe slots 121. When leakage of a magnetic flux through the gaps occurs,this correspondingly reduces a reluctance difference between the q-axisand d-axis directions.

However, there is a knit to reduction in the gaps between both the endsof the flux barriers 140 and the slots 121, namely, gaps between boththe ends of the flux barriers 140 and the conductive bars 122 embeddedin the slots 121. This is because, when the conductive bars 122 areformed in the slots 121 via, for example, aluminum die casting, toonarrow gaps have a risk of bursting under a pressure, causing moltenaluminum to be introduced into the flux barriers 140.

Accordingly, in order to achieve a further reduced gap with less risk ofbursting, it is preferable that both the ends of each flux barrier 140have a smaller width than that of the remaining portion of the fluxbarrier 140. Different embodiments related to the end shape of the fluxbarrier 140 are illustrated in FIGS. 5 to 7.

As will be understood from these embodiments, it is possible to minimizea length of the flux barrier 140 facing the adjacent slot 121. This hasthe effect of reducing an area that may burst upon receiving a pressure,and consequently, reducing the gap between the flux barrier 140 and theslot 121.

Meanwhile, the motor according to the present invention includes themagnets 130 arranged in the rotor core 123, to generate a magnetic fluxfor generation of magnetic torque.

The magnets 130, as shown in FIGS. 3 and 4, may be inserted into apartial region of the respective flux barriers 140. Of course, themagnets 130 may be inserted into all layers of the flux barriers 140, ormay be not inserted into a specific layer of the flux barrier 140.

Meanwhile, preferably, each flux barrier 140 is continuous in alongitudinal direction thereof, and at least two or more magnets 130 arepreferably arranged in the longitudinal direction of the continuous fluxbarrier 140. This is because it is very difficult to make a singlemagnet corresponding to the shape of the flux barrier. Furthermore,using a plurality of magnets is more efficient to minimize leakage of amagnetic flux generated from the magnets.

For the same reason, preferably, at least two or more magnets arearranged in a longitudinal direction of the rotor 120, namely, in aheight direction of the rotor 120.

On the basis of the above-described characteristics, the magnets 130 canbe composed of an identical shape of unit magnets, for example,bar-shaped unit magnets. This is advantageous to reduce manufacturingcosts of the magnets, and to facilitate easy manufacture of the motorwith a minimal variety of parts.

In addition, to determine insertion positions of the magnets 130 withrespect to each flux barrier 140, the flux barrier 140 is preferablyformed with a predetermined seating portion. Specifically, the fluxbarrier 140, as shown in FIGS. 9 and 11, is formed with a steppedportion 141, to determine insertion positions of the magnets 130. Theseating portion also serves to prevent unwanted movement of the insertedmagnets 130.

Meanwhile, preferably, an imaginary line, which connects correspondingtip ends of the magnets inserted in the respective layers of fluxbarriers, is parallel to the q-axis. With this arrangement of the tipends of the magnets, the greatest magnetic flux can be generated on thebasis of the q-axis. In addition, the total magnetic flux, generated byall the magnets, can take the form of a square wave rather than a sinewave.

The arrangement of the magnets enables generation of a greater magnetictorque on the basis of the q-axis and, as will be described hereinafter,permits an increase in a radial width of end-rings. The increased radialwidth of the end-rings has the effect of reducing loss due to thepresence of the end-rings.

Hereinafter, a motor manufacturing method, in particular, a rotormanufacturing method according to the present invention will bedescribed in detail with reference to FIGS. 8 to 14.

Referring to FIG. 8 illustrating configuration of a motor according tothe present invention, the rotor core 123 may include three differentshapes of unit rotor cores 124, 125, and 126. The orientation of themotor shown in FIG. 8 is suited to an upright drive motor.

Specifically, the rotor core 123 is a stack of unit rotor cores formedby stamping. The unit rotor cores may consist of the following threeshapes of unit cores.

First, the unit cores 125, which constitute an intermediate portion ofthe rotor core 123, can include all the above-described components,namely, the slots 121 for insertion of the conductive bars 122, a shafthole 128 for coupling of a rotating shaft (not shown), and the fluxbathers 140.

Next, as shown in FIGS. 8 and 9, the unit core 126, which constitutes alowermost portion of the rotor core 123, can include only the shaft hole128 and the slots 121. That is, the unit core 126 has no flux barrier.Accordingly, when magnets are inserted into a partial region of therespective flux barriers 140 of the unit cores 124 and 125, the unitcore 126 can prevent separation of the magnets.

Also, as shown in FIGS. 8 and 9, the unit core 124, which constitutes anuppermost portion of the rotor core 123, is formed with the shaft hole128, slots 121, and flux barriers 140. In this case, preferably, thereis provided a minimum of the flux barriers 140 required for insertion ofthe magnets, in consideration of the relationship with end-rings thatwill be described hereinafter.

Accordingly, after stacking the unit cores to obtain the rotor coreshown in FIG. 8, and then, forming end-rings via aluminum die casting,magnets can be inserted into the flux barriers. In addition, with theorientation of the motor as shown in FIG. 8, it is possible to preventscattering of magnets, via interaction between the interior of the rotorcore and the magnets, without a separate anti-scattering structure.

FIGS. 11 and 12 are a top plan view and a bottom plan view of the rotorcore having the above-described configuration. Specifically, accordingto the above-described rotor core, a general annular end-ring 151 asshown in FIG. 14 can be formed at the bottom of the rotor core.

Namely, the above-described rotor can be summarized as a rotor in whichmagnets are inserted after forming end-rings.

The general annular end-ring can be configured to cover the entire topsurface or bottom surface of the rotor core 123 except for the shafthole 128. Note that the greater the height and radial width of theend-rings, the smaller loss due to the end-ring. That is, similar toloss due to the conductive bar, the loss due to the end-ring can bereduced to the maximum extent.

However, increasing the height of the end-ring increases the size of themotor, and thus is limited. Accordingly, it is more preferable toincrease the radial width of the end-ring, in order to reduce loss dueto the end-ring.

Meanwhile, the uppermost unit core 124 shown in FIG. 8 can be replacedby the lowermost unit core 126 shown in FIG. 10. Specifically, theuppermost and lowermost unit cores can be replaced by the unit core 126shown in FIG. 10. The resulting configuration is an alternativeconfiguration of the motor according to the present invention.

In the alternative configuration, after stacking the intermediate unitcore 125 on the lowermost unit core 126, magnets are inserted into theflux barriers. Then, the uppermost unit core (in this case, identical tothe lowermost unit core) is stacked thereon, and conductive bars andend-rings are formed via aluminum die casting.

The above-described rotor core is shown in plan view of FIG. 12. Therotor core shown in FIG. 12 can use the general annular end-rings 151 asshown in FIGS. 12 and 14, which are provided at the top and bottomthereof.

More specifically, the above-described rotor can be summarized as arotor in which end-rings are formed after inserting magnets.Accordingly, the motor including the above-described rotor can preventscattering of magnets by the uppermost and lowermost unit cores, even ifit is not utilized in an upright drive manner.

Meanwhile, in the above-described configuration, the motor according tothe present invention always includes the end-rings, which do notinterfere with the magnets, but are connected with the plurality ofconductive bars 122. Of course, the end-rings do not interfere with theflux barriers 140.

More specifically, in an alternative configuration of theabove-described motor, the uppermost and lowermost unit cores of therotor core are not formed with the flux barriers 140, and thus, there isno interference between the end-rings and the flux barriers 140. Hence,the shape of the end-rings can be freely selected from all generalend-ring shapes, and this has the effect of minimizing loss due to theend-rings.

However, in the above-described configuration of the motor, the end-ring150 must be formed after completing the rotor core and prior toinserting the magnets into the flux barriers. In this case, it isimportant to eliminate any interference between the magnets and theend-ring 150. Namely, the end-ring 150 must be configured to have aspace for insertion of the magnets.

Here, to minimize loss due to the end-rings 150 as described above, itis preferable to increase the radial width of the end-rings 150.Therefore, preferably, the uppermost unit core 124 has a minimum of theflux barriers 140 required for insertion of the magnets.

In this case, the end-ring 150 can be configured to have a shape asshown in FIGS. 11 and 13. Specifically, the end-ring 150 can be dividedinto a q-axis direction portion and a d-axis direction portion, and awidth of the d-axis direction is larger than a width of the q-axisdirection. This is efficient to minimize loss due to the end-ring 150.In addition, since it is preferable to increase the width of the q-axisdirection portion of the end-ring 150, the flux barriers 140 are morepreferably configured to be converged toward the center of the rotor asshown in FIG. 11. Also, an inner circumference of the d-axis directionportion of the end-ring preferably extends in parallel to the q-axis.

Also, preferably, an inner circumference of the q-axis direction portionof the end-ring extends in parallel to the adjacent flux barrier.

Accordingly, in the above-described configuration, the end-ring 150 isan annular end-ring in which a radial width thereof varies along acircumferential direction of the rotor core 123. Moreover, the width ofthe q-axis direction of the end-ring is larger than that of the d-axisdirection portion.

Hereinafter, operation of the motor according to the present inventionwill be described in detail with reference to FIGS. 15 to 17.

The motor according to the present invention is basically applicable tovariable-load fan motors, compressors, bane electronics, etc.Hereinafter, for the convenience of description, a motor for use in arotary compressor will be described.

Generally, a rotary compressor mainly uses a single-phase inductionmotor, and thus, has a problem of low efficiency due to theabove-described characteristics of the single-phase induction motor.Hence, it will be appreciated that the motor according to the presentinvention is advantageously applicable to the rotary compressor, etc.,to improve the efficiency of the compressor.

Recently, a variable capacity compressor, in which a single rotarycompressor can carry out variable capacity operation, has been mainlyused.

As one example, there is a compressor capable of varying a capacity bychanging the quantity of a refrigerant to be compressed in a singlecylinder. This kind of compressor is disclosed in Korean PatentLaid-Open Publication No. 10-2006-0120387, wherein a refrigerant isselectively compressed in a plurality of cylinders to vary a capacity ofthe compressor.

Here, a capacity variation of the compressor means a variation of motorload for compression of a refrigerant. Accordingly, to achieve anoutstanding high efficiency of the variable capacity compressor, it isadvantageous to use the motor according to the present invention ratherthan a general induction motor.

This is because the motor according to the present invention is alwaysoperated at synchronous speed not only during normal operation, but alsoeven if motor load varies. In addition, since the motor is operatedusing reluctance torque and magnetic torque even if a temperaturethereof rises, it is possible to minimize loss due to temperatureincrease. It can be said that the above described effects are veryoutstanding effects in consideration of the facts that a generalsingle-phase induction motor suffers from serious loss due totemperature increase, and that the internal temperature of thecompressor significantly rises during operation of the compressor.

FIG. 15 illustrates the relationship between starting torque andcapacitor value.

As shown, the greater the capacitor value, the greater the startingtorque. Meanwhile, to initiate the starting of the motor, the startingtorque must be greater than a predetermined value. Namely, the startingtorque must have a value sufficient to overcome an initial motor load.Accordingly, if the initial motor load increases, the magnitude of thestarting torque required to overcame the motor load for the starting ofthe motor must be further increased.

Meanwhile, FIG. 3 illustrates a coil circuit having only a singlecapacitor. In this case, if motor load varies, the capacitor value mustbe increased to sufficiently overcame the motor load so as to start themotor. However, since using a high capacitor value under low motor loadcondition incurs loss, it is preferable that the capacitor value bevaried according to variation in motor load.

For this, the motor according to the present invention, as shown inFIGS. 16 and 17, may include capacitors connected in parallel.

Specifically, the coils include a main winding connected with asingle-phase power source, and an auxiliary winding connected parallelto the main winding while being connected to the single-phase powersource. Also, the capacitors, connected in parallel to each other, areconnected to the auxiliary winding in series. Mire specifically, thecircuit shown in FIGS. 16 and 17 can substitute for the capacitor shownin FIG. 3.

A value of the two capacitors, connected in parallel to each other, isequal to the total of the capacitor values when a switch S is kept on.Accordingly, when the switch S is turned on, a great capacitor value isobtained, resulting in a greater starting torque. Conversely, when theswitch is turned off, a value of only one capacitor is obtained,resulting in relatively small starting torque.

Accordingly, it is preferable that the switch be selectively turned onor off according to variation of the motor load, and more particularly,be turned on under high motor load and be turned off under low motorload.

For example, assailing that the compressor's capacity is divided into alarge capacity and a small capacity, FIG. 16 illustrates operation of alarge-capacity compressor, and FIG. 17 illustrates operation of asmall-capacity compressor. As can be seen from the drawings, it isadvantageous, in view of efficiency improvement, to not use a largecapacitor when the compressor has a low operation capacity.

Meanwhile, upon initial starting of the motor, namely, upon initialstarting of the compressor, the capacity of the compressor can bepreset. For example, the compressor can be preset to operate with alarge capacity or a small capacity.

Preferably, the motor is rapidly started to implement normal operation.To enable the rapid initial starting and at the same time, to achievebetter starting characteristics, it is preferable that the switch bekept on during initial starting of the motor. Namely, preferably, theswitch is always kept on regardless of the preset capacity.

More specifically, despite that the compressor is initially set tooperate with a snail capacity, if the compressor begins to operate whilekeeping the switch on and a desired time passes or a desired conditionis satisfied, it is preferable to turn off the switch. Conversely,despite that the compressor is initially set to operate with a largecapacity, if the compressor begins to operate while keeping the switchon and no operating condition is changed, it is preferable to keep theswitch on.

Note that the switch can be selectively turned on or off according tocapacity variation during normal operation.

Accordingly, the switch S can be selectively turned on or off on thebasis of whether or not the motor is started initially and whether ornot capacity varies during operation. This assures stable starting ofthe motor. In addition, a reduced initial starting time permits thecompressor to rapidly reach normal operation, resulting in improvedcompressor efficiency. This is because, as described above, the motoraccording to the present invention can rotate at synchronous speed usingreluctance torque and magnetic torque during normal operation, and canachieve extremely high normal operation efficiency.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

INDUSTRIAL APPLICABILITY

The present invention can provide a motor having improved efficiency anda variable capacity compressor including the motor.

1. A motor, in which a rotor is started using induction torque generated as power is supplied to a coil of a stator, wherein the rotor comprises: a rotor core; a plurality of conductive bars arranged, along a circumferential direction, in an outer rim region of the rotor core, to generate an induction current; a magnet provided in the rotor core, to generate a magnetic flux, for generation of magnetic torque; flux barriers formed in the rotor core, to interrupt flow of a magnetic flux, for generation of reluctance torque; end-rings provided at the top and bottom of the rotor core to have no interference with the magnet, the end-rings being connected with the plurality of conductive bars; a q-axis extending radially from a center of the rotor, along which the flow of a magnetic flux is interrupted by the flux barriers; and a d-axis extending radially from the center of the rotor, along which the flow of a magnetic flux is not interrupted, wherein the end-ring provided at the top of the rotor core includes a q-axis direction portion and a d-axis direction portion, and a radial width of the q-axis direction portion is smaller than a radial width of the d-axis direction portion.
 2. The motor according to claim 1, wherein the end-rings are provided to have no interference with the flux barriers.
 3. The motor according to claim 2, wherein the flux barriers are arranged to provide the rotor with two or more pairs of poles.
 4. The motor according to claim 1, wherein the rotor includes two pairs of poles, and the q-axis and the d-axis are spatially orthogonal to each other.
 5. The motor according to claim 1, wherein each flux barrier is symmetrical about the q-axis.
 6. The motor according to claim 5, wherein the flux barrier is tilted, about the center of the rotor, from the center to both ends thereof such that both the ends of the flux barrier are far away from or closer to an axis orthogonal to the q-axis.
 7. The motor according to any one of claims 2, 3, 4, 5 and 6, wherein the flux barriers that constitute each pole of the rotor are arranged in at least two or more layers.
 8. The motor according to claim 7, wherein the flux barrier of each layer is continuously formed.
 9. The motor according to claim 8, wherein the flux barriers, from the outside nearer to the inside of the rotor, have a longer length.
 10. The motor according to claim 1, wherein the magnet is inserted into a partial region of each flux barrier.
 11. The motor according to claim 10, wherein the rotor core is a stack of unit rotor cores.
 12. The motor according to claim 11, wherein uppermost and lowermost ones of the unit rotor cores have no flux barrier.
 13. The motor according to claim 12, wherein the end-rings, provided at the top and bottom of the rotor core, are annular end-rings having a constant radial width along the circumferential direction of the rotor core.
 14. The motor according to claim 13, wherein the end-rings are configured to cover the entire top and bottom of the rotor core except for a rotating shaft coupling region of the rotor core.
 15. The motor according to claim 11, wherein a lowermost one of the unit rotor cores has no flux barrier, and wherein an uppermost one of the unit rotor cores has a minimum of the flux barriers required for insertion of the magnet.
 16. The motor according to claim 15, wherein the end-ring, provided at the top of the rotor core, is an annular end-ring having a variable radial width along the circumferential direction of the rotor core.
 17. The motor according to claim 16, wherein the q-axis direction portion of the end-ring provided at the top of the rotor core is configured in parallel to the flux barriers.
 18. The motor according to claim 16, wherein the d-axis direction portion of the end-ring provided at the top of the rotor core is configured in parallel to the q-axis.
 19. A motor, in which a rotor is started using induction torque generated as power is supplied to a coil of a stator, wherein the rotor comprises: a rotor core; a plurality of conductive bars arranged, along a circumferential direction, in an outer rim region of the rotor core, to generate an induction current; a flux barrier formed in the rotor core, to interrupt flow of a magnetic flux, for generation of reluctance torque; end-rings provided at the top and bottom of the rotor core to have no interference with the flux barrier, the end-rings being connected with the plurality of conductive bars; a q-axis extending radially from a center of the rotor, along which the flow of a magnetic flux is interrupted by the flux barrier; and a d-axis extending radially from the center of the rotor, along which the flow of a magnetic flux is not interrupted, wherein the end-ring provided at the top of the rotor core includes a q-axis direction portion and a d-axis direction portion, and a radial width of the q-axis direction portion is smaller than a radial width of the d-axis direction portion.
 20. The motor according to claim 19, wherein a magnet is inserted into a partial region of the flux barrier. 